Rotary air compressor



y 1, 1954 s. A. HENDERSON 2,678,156

ROTARY AIR COMPRESSOR Filed Dec. 14, 1950 5 Sheets-Sheet l a.]NVENTOR.

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y 1954 s. A. HENDERSON ,678,156 ROTARY AIR COMPRESSOR Filed Dec. 14, 1950 5 Sheets-Sheet 2 INVENTOR. a.

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y 11, 1954 s. A. HENDERSON 2,678,156

ROTARY AIR COMPRESSOR Filed Dec. 14, 1950 5 Sheets-Sheet 3 w INVENTOR.

flz i arveys- May 11, 1954 s. A. HENDERSON 2,678,155

' ROTARY AIR COMPRESSOR Filed Dec. 14, 1950 5 Sheets-Sheet 4 wv Q; 90 1 3 A g 10 E -75 77-- I INVENTOR.

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y 11, 1954 s. A. HENDERSON 2,673,155

' ROTARY AIR COMPRESSOR Filed Dec. 14, 1950 5 Sheets-Sheet 5 za-w HIE mum BY H M flfforneys.

Patented May 11, 1954 UNITED STATVE'SPATENT OFFICE StanfordA. Henderson, Buffalo, N. Y., assignor to Gomco Surgical Manufacturing Corp., Buffalo, N. a corporation of New York Application December 14, 1950, Serial No. 200,765

1 l a This invention relates to improvements in rotary air compressors and more particularlylto such an air compressorfor use in dental oflices. ln most dental oilices there are tools and instruments which operate on compressed air. These tools and instruments are sometimes/used intermittently and it isessential that a supply of compressed air at the desired operating pressure, which is. usually from .20 to 40 pounds per square inch, be available at all times. At the present time the supply of compressed air is usually provided by a rather large unit which includes an electric motor, a. compressor driven thereby and a storage tank. The storage tankis required to maintain a suitable volume of compressed air at the desired pressure so that it will be immediately availablefor operating the tools or instruments when use thereof is commenced. The bulk of the presently used unit is so great that a considerable amount of oflice floor space is taken up and because of this the unit is sometimes placed outside the office and air lines are run into the interior of the ofiice from the remotely located storage tank. i

An. important object of the present invention is to provide a compressor unit of the type. described which is compact and occupies a small amount of floor spaceand can be readilymounted on a shelf or in a cabinet or closetor. any other desired place. 1 Another important object is to provide a rotary compressor which develops a relatively high pressure ina matter of seconds. t .Another object is toprovide such a. compressor which developssuch an immediate pressurethat the need for storage tanks for most installations .is eliminated. 1 fl H Another object is to provide such a compressor unitin which condensation of moisture from the compressed air. is reduced to a minimum. i M A further object is toprovide such a compressor which is self-lubricating, requires little maintenance, is not likely to get out of order or require repair and isrelatively inexpensiveto manufacture. r r Other objects and advantages of the invention will be apparent from the following description and accompanying drawings in which: .Fig. 1 is a diminutivewperspective view of a compressor unit embodying my invention. :Fig. 2 isan enlarged vertical transverse sectional view of the compressor shownwinFig. 1, the view being. taken on line2-2, Fig. 3..

Fig. 3 is a side view of the motorand compressor unit shown in Fig. 1,..the motor. being lci ms. (01. 230-152) shown in elevation and the compressor being shown in vertical central longitudinal section.

Fig. l is a vertical transverse sectional view of thecompressor and taken on line 4-4, Fig. 3.

i Fig. 5 is another vertical transverse sectional view thereof but showing the rotor in a different position, the view being taken on line 5-5, Fig. 3.

Fig. 6 is an enlarged fragmentary sectional view of one of the baflles in the stator of the compressor and taken on line B6, Fig. 4.

Fig. '7 is a vertical transverse sectional view of the compressor and taken on line 1-1, Fig. 3.

Fig. 8 is an enlarged side elevational view of the filter trap shown in Fig. 1.

Fig. 9 is a vertical central longitudinal sectional view thereof and taken on line 9-9, Fig. 8.

Fig. 10 is a horizontal transverse sectional view thereof and taken on 10-40, Fig. 9.

Fig. 11 is an enlarged fragmentary sectional view through the air intake of the compressor and taken on line ll-l I, Fig. 1.

Fig. 12 is an enlarged fragmentary sectional view through the compressed air outlet of the compressor and taken on line l2-l2, Fig. 1.

Fig. 13 is, a fragmentary plan view of the ports in the stator of the compressor and taken on line I3I3, Fig. 5.

Fig. 14 is a developed circumferential sectional view of the stator and taken on line I l-4 4, Fig. 5.

In accordance with the invention the compressor unit is shown as comprising generally an electric motor IS, a rotary air compressor l6 and a filter trap I1. The motor 15 may be of any suitable type and the compressor [6 is preferably arranged to form one end bell for the motor as shown, thus providing a compact unit which is resiliently mounted on the upturned arms of a U- shaped support l8 carried by a. base plate I9.

Therotary compressor [6 comprises .a stator including inner and outer cylindrical casings and zl respectively connected by an integral inner end head 22, and a removable outer end .head 23. A series of screws 21 are shown as securing the. removable outer end head 23 to the casing walls 2lland .21. Onthe side of the inner end head 22 opposite from the outer casing 21, the stator is formed with an axially extending cylindrical integral flange 24 which abuts against the housing of the motor 15. To mount the stator on the motor the flange 24 is interiorly formed with a series of circumferentially spaced bosses 25 which are provided with threaded holes to receiy longitudinal tie bolts 26 connected with the motor housing, as shown in Fig. 3.

,Tl ie armature shaft 23 of themotor i5 is shown as extending through the inner end wall 22 and into the compression chamber 29 surrounded by the inner cylindrical casing 20. The shaft 28 is shown as journaled in a sleeve bearing 30 carried by the inner end wall 22 and this bearing may be lubricated by an oil soaked bat of absorbent material 3| or in any other desired manner. Oil can be applied to the bat 3| through a vertical tube 32 leading to the exterior of the flange 24, as shown in Fig. 3.

The compression chamber 29 is cylindrical but has its axis arranged eccentrically withv respect to the axis of the shaft 28 as shown in Figs. 2,

r 4, and 7. A cylindrical rotor 33 is arranged within the chamber 29 so that its periphery is eccentric to the bore of this chamber and is nonrotatably mounted on the shaft 28. The rotor 33 is provided with a series of circumferentially spaced slots 34 which extend longitudinally the full length of the rotor and open to the periphery thereof. but; have their inner longitudinal ends terminating short of the shaft 28. Three such slots. 3.4 are shown. although any number desired may be employed. Ajblad'e, or vane 35- is slidingly arranged ineach slot 34- for radial movement, the outer longitudinal end; faces of these vanes engaging the cylindricalwall of the compression chamber 29 and the inner longitudinal end faces at all: times beingspaced from the bottoms of the slots for. a. purpose hereinafter described. The radial end: faces; of. the vanes 35 closely fit the opposing inner; end. faces of the end walls 22 and. 2.3. The5shaft28drives the rotor 33 to rotate in a clockwise direction as viewed in Figs. 2,. 4.

and 5.

Air is supplied. to. the Working spaces between adjacent pairs; of. vanes 35; to be compressed as the rotor 33 rotates. For this purpose, the inner and outer cylindrical? casings 20 and 2| respectively. of. thestator are spaced apart to provide an annular space which is. dividedoff by partitions 38: and 3.9:to provide an air inlet. chamber dd and a. compressedtair, outlet chamber 4|. The partitions. 38 and 39; are circumferentially spaced one from the other with the. lower: partition. 38 arranged: atabout a. seven ofclock position and the upper partition 33 at about a 12.0cl'ock positionas viewedinFigs. 2, 4 and5. The. partitions 38 and 39- arepreferably formed integrally with the inner and-outer casingsa20 and 21- respectively as shown.

A series ofcircumferentially' spaced radial baffles 42 are arranged in the air inlet chamber 60, two such bafiles being. shown with one arranged adjacent the partition 33and' the other adjacent the partition 39. As best shown in Fig. 14, the bafile 42' adjacent the partition 39 extends flush ,fronr the outer end faces of the casings 22 and 2|. longitudinally to. a point short of the inner end wall 22. soas to leave a. passage connecting the chambers on opposite sides of this bafile. Similarly but: in a reversed arrangement, the other baffle 42 adjacent the partition 38 projects axially outwardly from the inner end wall 22 and terminatesshort of the end faces of the casings 2.0 and 21 soas to leave a connecting passage between the chambers. on opposite sides of this baflie.

Air is admitted from the atmosphere into the air inlet chamber Bil through an inlet opening 43, This opening43 is arranged in'the removable cover or endwall23and'. communicates with that portion. of the 'chamber' 40 arranged between the upper partition 39 and the adjacentbafile 42 as shown in Fig..14. The air entering the inletopenthe air inlet chamber 40 with the compression chamber 28. The port 46 is arranged adjacent the lower partition 38 and between the same and the adjacent baifie 42. The inner end of the port 45 is enlarged and extends circumferentially principally in acounterclockwise direction from the port as shown at 48 in Figs..5 and 13.

An exhaust port 49 is arranged in the inner casing adjacent the intake port 66 and has its inner end also enlarged in a circumferential direction as. indicated at 50 in Figs. 5: and 13. The. circumferential. enlargement 5%; extends; in a clockwise direction from the exhaust port 49 as viewed in-.Fig..5. Thus as the rotor 33 rotates in. a clockwise. direction as viewed. in Fig; 5,. air passes through the intake port 43 intothe com.- pression' chamber 4.2 and pocketsor bodiesaof air are trapped between adjacent pairs of blades 35 and compressed during continued rotation of: the rotor and the compressed air is exhausted through the port 49 into the compressed air out.- let chamber ll.

The upper. part of the arcuate compressedzair outlet. chamber M is traversed by a. series of alternately staggered circumferentially spaced baffles 51:, four such baifles being shown. 'The uppermostbaiile. 5i begins flush with the coplanar outer faces of 'the. inner. and outer casings 23: and

2.! respectively and extends axially of. the'stator' terminating short of. the opposing face of; the inner. end'wall. 2.2. The next succeeding bafile 5| is reyersely arranged so that itextends. axially from the innerv end wall' 22 and terminates. short of the outer end wall 2 3.. In similar mannerthe succeeding bafiies 51 are alternately arranged. The. upper faces of these bafiies 51' are slanted downwardly towardtheir free radial ends. for drainage purposes as best shown; in. Fig. 6.,

An outlet 52:: for the compressed. air: in the chamber 4| is provided in'the removable cover. or

endwall 23. and is arranged. so. as to' communicate with this chamberbetween the partition 39 and the first adjacent baffle 5 I. A tubular conduit or pipe 53 is suitably connected at opposite-ends to the outlet 52 and. the inlet 54 of the filter trap 11.

It will be seen that the air inlet and outlet chambers Ml and "51 respectively are in the-form ofarcuate chambers ofsubstantial extent which surround the compression chamber 29. Also; theair inlet-43 and compressed air outlet 52v are conveniently arranged adjacent each other at the top of the stator. Further, the inlet 43 is at the trailing end of and theintake port 46 at theleading end of the arcuate air inlet chambertfl' while the outlet 52 is at the-leadingend of and theexhaust port 49 is at thetrailing end of'th arcuate compressed air outlet chamber 4|, relating the location of these openings to the 'unidirectionof rotation of the rotor 33. The-airis compelledto follow circuitous paths between respective-=sets of openings." I

7 An important featureof the'rotary compressor l fi 'is that'the fiuid pressure" on theinnerd outer longitudinal end face'sof-theblade's or varies 1 35 tends to be equalized at all times during oper-' ation oi thecompressorso that centrifugal force can act on these blades or vanes to urge the same outwardly against the surrounding wall of the compression chamber 23 and thereby insure a good seal betweenthis wall and these bladesor vanes. As previously described, the blades 35 never bottom in the slots 34 even when the vanes ar in their most retracted position as shown by the lowermost bladein Fig. 5b This leaves'a Iongitudinally extending chamber or spac under eachblade and the corresponding outer ends of these chambers communicate with a circular recess' 55 in the outer end face of the rotor33 as shownin Fig. 2. a

Referring toFig. 3, the annular recess 55 communicates with the inner end of a horizontal passage 56 which at its outer end communicates with a vertical passage 58. The passages 56 and 58.31am formed in the removable coveror' outer end wall 23 which is enlarged centrally to provide an outwardly projecting tubular neck 59 which surrounds a chamber. 60. This chamber 60 is formed as an axial recess in the tubular neck 59 and hasits inner end closed. The outer end ofxthechamber 6D. is closed by ajglass cover 6| held against the outer end face of the tubular neck 59;by .a removable ring 62.

if The upper endjofthe vertical passage 58 communicates with the chamber 60 and its lower end communicates with a filling hole 63. The filling hole 63 extends axially of the stator through the removable cover or outer end wall 23 so that the inner endqof this hole communicates with the lower part of the compressed air outlet chamber Ll. The 10111381 portion of this filling hole 63 is surroundedby a tubular neck 64 formed integrally with the end wall 23 and extending outwardly therefrom. The outer end of this tubular neck 64 is shown as arranged in an enlarged hole 65 in theadjacent upturned arm of the U-shaped support,;I8. 'A T fitting 66 is mountedon the outer end of the tubular neck 64 and has its lateral branch extending upwardly and closed by a removable plug 68. A screw plug 69 closes the outer end of the T. fitting 66. The interior passages of the T fitting 66 communicate with t e fill h 5 it a l Thus it will be seen that if eitherplug 68 or 661 is. removed, hydraulic fluid such as oil can be forced into the compressed air outlet chamber 4|, thepassages 63, 58, and 56, the chamber 66, the annular groove 55 and the spaces at the bases of the slots 34 unoccupied by the blades 35. Sum-.- cient oil'is inserted so that a body II! is provided in the bottom of the compressed air outlet chamher and the passages 63, 58, 56, groove 55 and the chambers at the bases of the slots are comp1ete1y filled, While the chamber to need not be completelyfilled. 1 Referring to Fig. 5 it will be seen that the compressed air discharged from the exhaust port-.143 is in direct contact with the bodyof oil I0. andthereby transmits its pressure to it. pressure is transmitted: through the stationary passages 63, 58 and 56 to the annular groin/e155 on the rotor which in turn transmits the pressure to the slots 34 and the inner longitudinal ends of the blades 35. Sincethe bases of the slots 34 are interconnected through the annular groove 55, oilcan be displaced from any slotand fed to any other slot as will occur when the blades '35 move radially in and outer theirslots during r0:- tation of. the rotor;- iThehorizontal.passage 56 is of relatively small diameter so that interflow be tween the slots 34 is promoted.

The bodyof oil 16 may become agitated by the compressed air discharged by the exhaust port 49 and thus cause this oil to foam up. If oil with entrained air bubbles works into the vertical passage 58 the air bubbles will rise into the chamber 60 passing the entrance to the horizontal restricted passage 56. In this way the oil admitted to the rotor is purged of air. Also, a sufiicient'body of l oil is maintainedv in the chamber Bill to serve as a reservoir to insur a constant supply of oil to the slots 34.

Inasmuch as the blades 35 have a sliding fit in the slots 34, some of the pressurized oil at the inner ends of these blades will work out radially andlongitudinally of the slots and serve to lubricate the sliding surfaces.

i It will be seen that the entrapped air between adjacent pairs of blades 35 will tend to leak past the sliding joint between the outer longitudinal end faces of the blades and the Wall of the compression chamber 2a which they engage; How'- ever, such leakage is defeated by reason of the pressurized oil pressing against the inner-longitudinal end faces of the blades 35 and urging these. blades into a firm contact with the wall. The pressure of the oil will be always at least equal to the pressure of the air so tryingto leak past the vanes 35. Moreover, centrifugal. force working on the vanes 35 urges them outwardly into still firmer engagement with the compression chamber wall so that there is always a preponderant forc urging the vanes outwardly regardless of the pressure of the compressed air and oil.

. Leakage of compressed air past the vanes has been a defect of rotary compressors as heretofore constructed and it will be seen that my rotary compressor effectively overcomes this undesirable condition and also makes possible a. compressor of smaller size for a given pressure rating.

It-will also be seen that any entrained oil in the compressed air discharged by the exhaust port 49 will be separated from the air by reason of the fact that the compressed air is caused to follow a circuitous path back and forth past the baflles. 5| as it moves toward the outlet 52. The successive and sudden reversals ofair flow will tendto separate the compressed air andentrained oil. The so separated oil collects along the upper slanted sides of the baiiles 5| and drains off the radial free edge thereof onto the next lower bafiieand so on until the separated oil rejoins the main body of oil 10 in. the bottom of the stator. 5

While the compressor and motor unit may be mounted on the U-shaped support I18 in any suitable manner, it is shown as resiliently mounted at opposite ends by a rubber ring ll clamped by a strap device 12 to the correspondingupturned arm of the support I8, as shown in Figs. 1 and 3. Referring to Figs. 8-10, the filter trap I1 is shown as comprising a cylindrical tubular body 15, an upper, end head 16 and a lower endhead 11. The opposite ends of the tubular body '15 seat against gaskets 18 arranged in annular recesses provided in the end heads 16 and TI. The end 'heads 16 andl'l are held firmly on the tubular body 15 by a tie bolt 19 arranged centrally within the tubular body and which extends longitudinally thereof, the upper threaded endof the tie bolt .being screwed into a threaded recess the horizontal inlet 54 and a horizontal outlet.

8|v on: opposite lateral sides,v a front horizontal. passage which communicates with a pressure gauge 82' and a vertical passage which communi' cates. with a pressure. switch 83. The gauge. 82 and; switch 83 are. suitably mounted on the up-- per end head it. The pressure switch 83 may be:

oi": anysuitable type and is electrically connected 7 with: thelelectric motor throughthe: line -'84 and. has foritsfunction to energize and deenergize the motor in accordance with a predetermined setting of the switch for; a particular. desired-pressure of compressed air within the filter trap H. Thus when. the pressure within. the filter trap drops below the predetermined settingv the pressure-switch 83; operates to energize the motor 15 by connecting the line 84 with a.current4supp1y line 85. Onthe other hand when: the pressure within the filter trap exceeds the. said predetermined setting the pressure switch 83 operates to interrupt current flow to the motor'l5.

The hollow interior'of the filter trap-is'divided into a relatively small upper chamber 86 and a largerlower chamber 88 by a filter disk '89. This filter. disk 89 may be made of any suitable material such as fiberglass and has its periphery closely fitting the wall of the tubular body 15 and is held on the tie rod 19 which. extends through it in any suitable manner as by the clip Bil; This clipllfl is shown as having legs biased toward each other and arranged on opposite sides of the tie rod 79 so as to clamp the clip-on this rod, the filter disk 89 resting on theclip and being supported thereby.

Compressed air entering the filter trap I! through the inlet 54 is led to the lower chamber 88 by the tube 9|. This tube 9| open. at both ends is shown as extending vertically through a closely fitting hole in-the-filter-disk 89 being screwed into a threaded hole in the upper end head 76' which communicates with the inlet -54.

The compressed air so discharged into the lower chamber 88 is likely to contain volatile matter which condenses inthis chamber, collectingin the=bottom thereof. The compressed air escapes through the disk filter 89 to the upper chamber 86 andenters the outlet 8| towhich a line 92 can be connected. This line 92- leads to the desired tool; instrument or equipment to be operated on compressed air; Condensate can be withdrawn from the lower chamber 88 from time to time by a drain cook 93 shown-as mounted on the lower end head! i.

'A' 'fitting 94 is shown in Fig. 9 as mounted on the-upper end head 16 to connect the conduit 53 withlthe inlet 54-. A check'valve 95 is'p referably arranged in the fitting 94 and the same is shown as a disk seating against a shoulder 96 facing the inlet and urged thereagainst by a coilspring 98. Thus the check" valve 95 prevents back flow of compressed air from the filter trayi'l to the compressor it when the rotor I5 is not running. However, this valve disk 95'is lifted off its seat 96. against the urging of the spring 98 when-the compressor is delivering compressed air. to the filter trap.

' Primarily the purpose of the filter trap. H is to rcondense'the volatile components inithe'corne 8; pressedairrand secondarily to. provide" a smallt storage space for the compressed air. However.-. the-volume of compressed air held. inthefilter trap is very small. compared with the relativelymuch larger storage tank employed. with con.- ventional compressor units presently used;

' The upper end'heads16 is shown as providedat its rearwith an-upstanding; flange 99 having; holes. to receive screws i00 whereby the filter trap can beconveniently mounted on anysuit:- able" support. 7 7

It will be noted that the double casingjwalls 2S- and 2t connected by" the partitions 38 and: 3.91 and the baffles 42 and 5i. provide an extene. sive surface for radiation of heat developedfrom'. compressing the air in' the. compressor. This effective: way of dissipating the heat developed reduces the temperature of the cornpressedairdelivered.- to the filter trap l1" and. hence minimediately available compressed air at relatively high pressure.

While the invention has been described: with; particular reference to apparatus. for adent'al oiiice, it will be understood that this is. illustrative and not limitative of the invention.

I claim: 7

1'. A- rotary compressor, comprising a stator. having inner and outer spaced annular casing: walls, a compression chamber surrounded'by. said inner casingwall, partitions connecting said inner'and outer casing walls and spaced one from the other to provide air inlet and outlet chambers each of substantial circumferential extent, rotary means arranged within said compression chain her for compressing air therein, means-providing an intake port connecting said inlet andcompression chambers only at the leading end of said inlet chamber, means providing an air inlet to said inlet chamber only at the trailing end thereof, means providing an exhaust port con-- necting said outlet and compression chambers only at the trailing end of said outletchamber, means providing acompressed air outlet from saidoutlet chamber only at the leading-end thereof, and bafiies arranged in said inlet and outlet chambers and extending generally longitudinally of said stator and connecting said inner and;outer casing walls and alternately staggered-to. pro,

5 vide acircuitous path for theair flowing fromv said inlet to said intake port; and alsoacircuitous pathforthe compressed air flowing'from said exhaust port to said outlet.

2;. A rotary compressor, comprisinga stator having inner and outer spaced annular casing walls, .a-compression chamber surrounded by said inner; casing wall, partitions connecting saidinner andouter casing walls and spaced one from the other to provide airv inlet and outlet chambers;

each of substantialcircumferential extent, rotary means arranged within said compression cham berfor' compressing air'therein, means providing an intake'port connecting said inletand com? pression'chambers only at the leading end of said inlet" chamber, means providing an airinlet to said inletchambe-r-only at the trailingend-there of, means providing an exhaust port connecting said outletand compression chambers: only at the. trailing: end. of; said outlet: chamber; means 1pm.? viding;a..-.compressed air outlet. from. said outlet chamber only at the leading end thereof, a filter device filtering air entering said inlet chamber through said inlet, and fibrous material arranged in said inlet chamber to filter air flowing therethrough from said inlet toward said intake port.

3. A rotary compressor, comprising a stator having inner and outer spaced annular casing walls arranged with their axes generally horizontal, a compression chamber surrounded by said inner casing wall, rotary means arranged within said compression chamber for compressing air therein and including a slotted rotor and blades movably arranged in such slots, partitions connecting said inner and outer casing walls adjacent the top and bottom thereof to provide separate air inlet and outlet chambers of substantial circumferential extent, a body of oil contained within the bottom of said outlet chamber, passage means connecting said oil body with the inner ends of said rotor slots in all rotative positions of said rotor, said inner casing wall being provided with an exhaust port above the level of said oil body and connecting said outlet and compression chambers and serving to impose the pressure of the compressed air discharged through said exhaust port on said oil body so as to fill said passage means and said inner ends of said slots with such oil, means providing a compressed air outlet from said outlet chamber at the upper endthereof and remote from said exhaust port, bailies arranged in said outlet chamber at circumferentially spaced intervals and extending generally longitudinally of said stator and connecting said casing Walls and alternately staggered to provide a circuitous path for the compressed air flowing from said exhaust port to said outlet whereby oil entrained in said compressed air is urged to separate therefrom and allowed to drain down to said oil body, said inner casing wall being provided with an intake port connecting said inlet and compression chambers, and means providing an air inlet to said inlet chamber circumferentially remote from said intake port.

4. A rotary compressor as defined in claim 3 in which said bafiies extend radially between said inner and outer casing walls and have their upper surfaces sloping downwardly in a direction longitudinally of said stator toward their free edge to facilitate the draining of oil.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,462,842 Aikman July 24, 1923 1,780,156 Hall Nov. 4, 1930 1,780,583 Evans Nov. 4, 1930 1,928,300 Peltier Sept. 26, 1933 2,057,381 Kenney et al Oct. 13, 1936 2,289,441 Le Valley et al July 14, 1942 2,411,602 Iweedale Nov. 26, 1946 2,455,297 Curtis et a1 Nov. 30, 1948 2,460,814 Duerr, Jr. Feb. 8, 1949 2,467,408 Semon Apr. 19, 1949 2,498,973 Whiteley Feb. 28, 1950 2,544,988 Gardiner et al Mar. 13, 1951 2,575,074 Senninger Nov. 13, 1951 

